[test] Make test filters platform-independent.

tools/run-tests.py

 #!/usr/bin/env python
 #
 # Copyright 2012 the V8 project authors. All rights reserved.
 # Redistribution and use in source and binary forms, with or without
 # modification, are permitted provided that the following conditions are
 # met:
 #
 #     * Redistributions of source code must retain the above copyright
 #       notice, this list of conditions and the following disclaimer.
 #     * Redistributions in binary form must reproduce the above
@@ skipping 487 matching lines @@
       return [name]
   args = reduce(lambda x, y: x + y,
          [ExpandTestGroups(arg) for arg in args],
          [])
 
   if len(args) == 0:
     suite_paths = [ s for s in DEFAULT_TESTS if s in suite_paths ]
   else:
     args_suites = OrderedDict() # Used as set
     for arg in args:
-      args_suites[arg.split(os.path.sep)[0]] = True
+      args_suites[arg.split('/')[0]] = True
     suite_paths = [ s for s in args_suites if s in suite_paths ]
 
   suites = []
   for root in suite_paths:
     suite = testsuite.TestSuite.LoadTestSuite(
         os.path.join(workspace, "test", root))
     if suite:
       suites.append(suite)
 
   if options.download_data or options.download_data_only:
@@ skipping 174 matching lines @@
   exit_code = runner.Run(options.j)
   overall_duration = time.time() - start_time
 
   if options.time:
     verbose.PrintTestDurations(suites, overall_duration)
   return exit_code
 
 
 if __name__ == "__main__":
   sys.exit(Main())